Recently, a projection type image display apparatus (hereinafter, referred to as a projector) using an LED, a laser, or the like has been developed, and a small size portable projector is expected.
In particular, a small size scanning type projector combining lasers of three primary colors and a MEMS (Micro Electro Mechanical Systems) mirror has been developed because it requires fewer parts or components and the possibility of microminiaturization (see, for example, Japanese Patent Number 4031481).
FIG. 22 shows such a conventional scanning type projector having the three primary color lasers and the MEMS mirror. The projector shown in FIG. 22 has semiconductor lasers 1-R, 1-G, and 1-B configured to emit laser light of red R, green G, and blue B, respectively, lenses 2-R, 2-G, and 2-B configured to focus the laser light emitted from the semiconductor lasers 1-R, 1-G, and 1-B, respectively, dichroic mirrors 3-R, 3-G, and 3-B configured to reflect only red light, green light, and blue light and transmit light of the other colors, respectively, a MEMS mirror device 501 having a mirror configured to have a variable inclined angle, and a control device 502 configured to allow the mirror of the MEMS mirror device 501 to be rotated or turned in horizontal and vertical directions and to allow the semiconductor lasers 1-R, 1-G, and 1-B to emit laser light which has a light intensity modulated according to input video signals.
The control device 502 has a mirror control section and a modulating section and an image is formed on a screen 503 by modulating laser light intensity in synchronism with the angle of the MEMS mirror device 501.
In such a method of combining color light, the focusing lens is necessary for each laser so that the number of parts and components is increased and a small size and lightweight device cannot be achieved.
FIG. 23 shows an example where light fluxes from three color light sources of red, green, and blue 601R, 601G, and 601B are combined by a dichroic prism 602 and focused by a focusing lens 603 (see, for example, Japanese Patent Application Publication Number 2001-154607).
In such a configuration, although only one focusing lens is used, the light sources are arranged such that the emitting directions of the light sources are different from each other so that there is a disadvantage in achieving a small size and lightweight device.
FIG. 24 shows an example where light fluxes from two light sources are emitted in the substantially same direction and coupled by one coupling lens and combined and emitted on one light path via a two-beam combining prism, and therefore light from a plurality of light sources is combined and emitted on one light path.
This example relates to a pickup optical system of an optical disk, and a semiconductor laser 1011 of a wavelength of 660 nm and a semiconductor laser 1012 of a wavelength of 780 nm are changed into substantially parallel light fluxes by a collimating lens 1020 and a two beam combining prism 1031 is configured to match optical axes of the light flux of 660 nm and the light flux of 780 nm with each other, to enter an objective lens.
For the collimating lens used for the light pickup of the optical disk, in order to focus narrowly the light on a spot of a recording surface of the optical disk (1061, 1062) without variation, it is required to ensure a sufficient intensity in a distribution of light intensity of the light entering an edge of the objective lens 1050 in relation to a peak intensity of the laser light source so that the focal length of the collimating lens cannot be reduced.
When the focal length of the collimating lens is large (about 10 mm or more), an efficiency of coupling the light from the light source is decreased and the light use efficiency is reduced.
Furthermore, the large size of the apparatus cannot be prevented because of the large focal length. If the focal length of the collimating lens is set to be small, it is difficult to remove astigmatism generated in the light reflected on a rear surface of the two beam combining prism under practical conditions such as an interval between the two light sources, and thickness of the two beam combining prism. Accordingly, it is difficult to combine light fluxes from the two light sources by one collimating lens of small focal length. Conventional technology is also described in Japanese Patent Application Publication Number 2002-207110.
As described above, it is difficult, by use of one collimating lens of a small focal length, to combine light fluxes from a plurality of light sources with good wave front onto one light path via a two beam combining prism by allowing the two light sources to emit light fluxes in the substantially same directions and allowing one coupling lens to couple the light fluxes, as described in the conventional technology.